Non-Invasive Techniques Reveal Heifer Response to Fescue Endophyte Type in Grazing Studies

Abstract

Cattle grazing tall fescue (Schedonorus arundinaceous) infected with wild-type endophytes (WE) leads to a syndrome commonly known as fescue toxicosis. Replacing WE tall fescue with a novel endophyte-infected (NE) tall fescue can mitigate this problem but adoption of this technology has been limited. This study measured and determined the physiological and behavioral responses of heifers that grazed either WE or NE tall fescue, utilizing relatively non-invasive techniques including hair cortisol, thermography (for extremity temperatures), small loggers for intravaginal temperature, and remote observation of in-field behavior. Heifers that grazed WE had greater (p < 0.0001) hair cortisol levels, lower extremity temperatures (p ≤ 0.0075), and 0.3-0.9 °C greater (p ≤ 0.02) intravaginal temperatures (particularly during the daytime) than heifers that grazed NE. From 1200 h-1700 h each day, heifers on WE pastures spent 1.5 more (p = 0.0003) hours standing up and 0.9 fewer (p = 0.0402) hours lying down than heifers on NE pastures. Differences (p = 0.0160) in ADG were small (0.1 kg d^-1) and were only observed in the first year of these 8-week studies. However, even in the mild environment of the study site, grazing NE tall fescue provided clear welfare benefits as evidenced by heifer behavioral changes, temperature differentials, and hair cortisol levels. This study underscores the potential utility of non-invasive techniques, such as thermographic imaging and hair cortisol analysis, for evaluating animal responses to stress in extensive grazing systems.

Keywords: cortisol; fescue toxicosis; stress; thermography; vasoconstriction.

Figure 1

Daily average, minimum, and maximum temperatures (°C) and precipitation (mm) throughout the study period at Southwest Agriculture Research and Extension Center, Glade Spring, VA, USA.

Figure 2

Daily average temperature-humidity index (THI) throughout the study period at Southwest Agriculture Research and Extension Center, Glade Spring, VA, USA.

Figure 3

Average temperature-humidity index (THI) by hours during the intravaginal temperature and heifers’ behavior data collection dates for 2020 and 2021 at Southwest Agriculture Research and Extension Center, Glade Spring, VA, USA.

Figure 4

Comparison of mean vaginal temperatures (SE- 0.10) of heifers that grazed either toxic (WE) or novel endophyte (NE) infected tall fescue by the hour of the day. Level of significance: * p < 0.05, ** p < 0.01, *** p < 0.001.